The present invention relates to an optical parallel transmission transmitter/receiver used for optical communication, and an optical module substrate having optical elements (light-receiving element/light-emitting elements) and optical fibers.
Along with an increase in required transmission capacity, the optical parallel data transmission technology for optical communication systems is becoming promising. An optical communication system using the optical parallel data transmission technology is divided into three sections: a transmission section, optical fiber transmission line, and reception section. In the transmission section, a plurality of electronic signals forming a bit sequence are input, subjected to signal processing, waveform shaping, and amplification, and output as optical signals through a current driving circuit and light-emitting element. In the reception section, the optical signals are converted into electrical signals by light-receiving elements, and the signals are subjected to amplification and signal processing to restore the original electrical signal bit sequence (Latest Materials of Optical Communication Technology III, xe2x80x9cOptical parallel Data Transmission Scheme and Hardware Configurationxe2x80x9d, pp. 191-192).
To realize an optical communication system using the optical parallel data transmission scheme, it is necessary to {circle around (1)} accurately and easily align the optical axes of an optical element array and optical fiber array and fix them, and {circle around (2)} hermetically seal the optical element array which readily degrades due to a change in humidity or temperature. A technique is known for this purpose in which a bundle fiber is inserted between a plurality of optical elements and a plurality of optical fibers to optically couple the optical elements to the optical fibers (Japanese Patent Laid-Open No. 5-188250).
Additionally, as described in transactions xe2x80x9cthe 1995 IEICE Conference C-185xe2x80x9d, a structure is known in which a V-groove is formed in the upper surface of a silicon substrate, a light-emitting element is positioned and fixed at a predetermined position on the distal end side of the V-groove, and an optical fiber is arranged in the V-groove, thereby matching the optical axes of the optical fiber and light-emitting element.
From the viewpoint of facilitation and automation of the manufacturing process, a structure has been proposed in which optical coupling to light-emitting elements or light-receiving elements is achieved using a ferrule in which optical fiber strands are inserted and fixed (Japanese Patent Application No. 9-83004).
As an element technique for optical parallel transmission, for example, Japanese Patent Laid-Open No. 7-209556 discloses an optical transmission/reception module which integrates an LD (Laser Diode) array, PD (PhotoDiode) array, optical fiber array for optically coupling the LD array and PD array, LD IC, and PD IC. In this optical transmission/reception module, to facilitate alignment between the LD array, the PD array, and the optical fiber array, an optical module substrate made of silicon and having a plurality of V-grooves is used, and the optical fiber is formed by inserting a plurality of optical fibers into the V-grooves in the optical module substrate. Silicon is used for the optical module substrate because working of V-grooves can be easily and accurately realized.
However, when a plurality of optical fibers and a plurality of optical elements (light-receiving elements or light-emitting elements) are to be optically coupled using the conventional system, operation becomes hard. For, e.g., a 12-fiber array, operation is greatly complicated unless shift due to rotation is taken into consideration, unlike a case wherein a single optical fiber is connected to an optical element.
In addition, when not only an optical fiber array but also a light-emitting element array (e.g., a laser array) or light-receiving element array is mounted on an optical module substrate, the alignment operation is to be further facilitated, and the size of light-emitting module or light-receiving module is to be reduced, the optical module substrate according to the prior art has the following problems.
A laser beam emitted from each of a plurality of exit regions of a laser array diverges to some extent. For this reason, when the laser array is mounted on the mounting surface of an optical module substrate, the laser beam emitted from each exit region is partially reflected by the mounting surface of the optical module substrate. As a consequence, the coupling efficiency of the optical fibers of the optical fiber array lowers, and light reflected by the mounting surface generates noise.
Leakage light from a reflection region opposing each of the plurality of exit regions is also reflected by the mounting surface. As a consequence, the light reflected by the mounting surface generates noise.
When a light-emitting element array or light-receiving element array is to be mounted on an optical module substrate, normally, printed interconnections for electrically connecting the light-emitting element array and driving circuit and the like, or the light-receiving element array and amplification circuit and the like must be formed on the optical module substrate. Especially, when the optical module substrate is formed from a conductive material such as silicon, interconnections cannot be directly formed on the surface by metallizing. hence, an insulating film is formed on the surface, and interconnections are formed on this insulating film. With this arrangement, however, operation errors occur in the light-emitting module due to the parasitic capacitance generated between the interconnections and the optical module substrate through the insulating film, or noise is generated in the light-receiving module.
It is an object of the present invention to provide a structure capable of easily realizing operation of optically coupling a plurality of optical fibers and a plurality of optical elements. It is another object of the present invention to provide an optical module substrate which prevents any operation error of a light-emitting module or reduce noise in a light-receiving module.
In order to achieve the above object, according to the present invention, there is provided an optical parallel transmission receiver in which a plurality of light-receiving elements and a plurality of optical fibers are optically coupled via guide pins, characterized by comprising a pair of guide pins, fiber holding means (e.g., a ferrule) for holding the pair of guide pins in parallel and holding the plurality of optical fibers (e.g., a tape-like optical fibers) between the pair of guide pins at a predetermined interval, and light-receiving element holding means for holding the plurality of light-receiving elements (e.g., a light-receiving element array) between the pair of guide pins and holding one end of each of the pair of guide pins so as to make a plane including light-receiving surfaces of the light-receiving elements perpendicular to longitudinal axes of the guide pins, wherein the fiber holding means and the light-receiving element holding means are integrally held by resin molding.
There is also provided an optical parallel transmission transmitter in which a plurality of light-emitting elements and a plurality of optical fibers are optically coupled via guide pins, characterized by comprising a pair of guide pins, fiber holding means for holding the pair of guide pins in parallel and holding the plurality of optical fibers between the pair of guide pins at a predetermined interval, and light-emitting element holding means for holding the plurality of light-emitting elements between the pair of guide pins and holding one end of each of the pair of guide pins so as to align optical axes of the light-emitting elements with core axes of the optical fibers, wherein the fiber holding means and the light-emitting element holding means are integrally held by resin molding.
According to the present invention, there is also provided an optical parallel transmission receiver in which a plurality of light-receiving elements and a plurality of optical fibers are optically coupled via a pair of guide pins, characterized by comprising light-receiving element holding means for holding the plurality of light-receiving elements and holding one end of each of the pair of guide pins so as to make light-receiving surfaces of the light-receiving elements cross core axes of the optical fibers, wherein the light-receiving element holding means is formed from an insulator.
The light-receiving element holding means may comprise a light-receiving element array in which the plurality of light-receiving elements are arranged in an array, a preamplifier IC connected to the light-receiving element array and including a plurality of reception circuits, and a heat-conductive lead frame which is in contact with the preamplifier IC at one part and has a heat dissipation portion formed at the other part.
The light-receiving element holding means may comprise a guide pin holding portion for holding the guide pins, a first holding portion for holding the light-receiving element array, and a second holding portion for holding the preamplifier IC, the first holding portion may be positioned with reference to the guide pin holding portion, and when the light-receiving element array is held by the first holding portion, the light-receiving element array may be positioned with respect to the guide pins to be inserted to the guide pin holding portion.
The light-receiving element holding means may comprise a first plate member and a second plate member, which sandwich the lead frame, the first plate member having a pair of through holes which form the guide pin holding portions, and a pair of opening portions which expose part of the lead frame and form the first holding portion and the second holding portion.
The light-receiving element array may comprise back-incident-type light-receiving elements each having a light-receiving surface on an opposite side of a surface having an electrode connected to the preamplifier IC, the first holding portion may have an opening extending to a back side of the light-receiving element holding means, the back-incident-type light-receiving elements may be arranged to make the light-receiving surfaces expose to the back side of the light-receiving element holding means, and the plurality of optical fibers may be optically coupled to the light-receiving surfaces of the back-incident-type light-receiving elements through the pair of guide pins on the back side of the light-receiving element holding means.
According to the present invention, there is provided an optical parallel transmission transmitter in which a plurality of light-emitting elements and a plurality of optical fibers are optically coupled via a pair of guide pins, comprising light-emitting element holding means for holding the plurality of light-emitting elements and holding one end of each of the pair of guide pins so as to arrange optical axes of the light-emitting elements and core axes of the optical fibers, wherein the light-emitting element holding means may be formed from an insulator.
The light-emitting element holding means may comprise a light-emitting element array in which the plurality of light-emitting elements are arranged in an array, a driver IC array connected to the light-emitting element array and having a plurality of driving circuits, and a heat-conductive lead frame which is in contact with the driver IC array at one part and has a heat dissipation portion formed at the other part.
The light-emitting element holding means may comprise a guide pin holding portion for holding the guide pins, a first holding portion for holding the light-emitting element array, and a second holding portion for holding the driver IC array, and a light-receiving element may be arranged between the first holding portion and the second holding portion.
The light-emitting element holding means may comprise a first plate member and a second plate member, which sandwich the lead frame, the first plate member having a pair of grooves which form the guide pin holding portion, and a pair of opening portions which expose part of the lead frame and form the first holding portion and the second holding portion.
The light-emitting element array may be mounted faceup on the lead frame via an insulating submount.
The lead frame may be separated into two parts which are held by the first plate member and the second plate member while being spaced apart at a predetermined interval, and the light-emitting element array may be mounted on one part of the lead frame while the driver IC array may be mounted on the other part of the lead frame.
The light-emitting element holding means may comprise a guide pin holding portion for holding the guide pins on one surface, a first holding portion for holding the light-emitting element array, and a second holding portion for holding the driver IC array, and the driver IC array having a plurality of driving circuits may be in contact with the light-emitting element holding means.
According to the present invention, there is also provided an optical module substrate for mounting a laser array having a plurality of emission regions, and an optical fiber array formed by arraying a plurality of optical fibers optically coupled to the plurality of emission regions, respectively, characterized in that a groove portion is formed in a mounting surface for mounting the laser array at a portion corresponding to each of the plurality of emission regions of the laser array.
When the groove portion is formed in the mounting surface for mounting the laser array at a portion corresponding to each emission region, reflection of a laser beam emitted from the emission region by the mounting surface is reduced.
According to the present invention, there is provided an optical module substrate for mounting a laser array having a plurality of emission regions, and an optical fiber array formed by arraying a plurality of optical fibers optically coupled to the plurality of emission regions, respectively, which may be characterized in that a groove portion is formed in a mounting surface for mounting the laser array at a portion corresponding to each of a plurality of reflection regions respectively opposing the plurality of emission regions of the laser array.
When the groove portion is formed in the mounting surface for mounting the laser array at the portion corresponding to each reflection region, reflection of leakage light leaking from the reflection region by the mounting surface is reduced.
According to the present invention, there is also provided an optical module substrate for mounting a laser array having a plurality of emission regions, and an optical fiber array formed by arraying a plurality of optical fibers optically coupled to the plurality of emission regions, respectively, which may be characterized in that a groove portion is formed in a mounting surface for mounting the laser array at a portion corresponding to each of the plurality of emission regions of the laser array and a portion corresponding to each of a plurality of reflection regions respectively opposing the plurality of emission regions of the laser array.
When the groove portion is formed in the mounting surface for mounting the laser array at the portion corresponding to each emission region, reflection of a laser beam emitted from the emission region by the mounting surface is reduced. In addition, when the groove portion is formed in the mounting surface for mounting the laser array at the portion corresponding to each reflection region, reflection of leakage light leaking from the reflection region by the mounting surface is reduced.
According to the present invention, there is also provided a light-emitting module characterized by comprising a laser array having a plurality of emission regions, an optical fiber array formed by arraying a plurality of optical fibers optically coupled to the plurality of emission regions, respectively, an optical module substrate for mounting the laser array and the optical fiber array, a driving circuit for driving the laser array, and a base for mounting the optical module substrate and the driving circuit, wherein the optical module substrate comprises any one of the above optical module substrates.
When any one of the above optical module substrates is used, reflection of a laser beam emitted from the emission region of the laser array by the mounting surface is reduced, or reflection of leakage light leaking from the reflection region of the laser array by the mounting surface is reduced.
According to the present invention, there is also provided an optical module substrate for mounting a light-emitting element array formed by arraying a plurality of light-emitting elements and an optical fiber array formed by arraying a plurality of optical fibers optically coupled to the plurality of light-emitting elements, respectively, characterized in that the optical module substrate is formed from an insulating ceramic.
When the optical module substrate is formed from an insulating material, no insulating film need be formed between printed interconnections and the optical module substrate, and a parasitic capacitance is prevented. In addition, when the optical module substrate is formed from a ceramic, the workability and working accuracy are ensured.
According to the present invention, there is also provided an optical module substrate for mounting a light-receiving array formed by arraying a plurality of light-receiving elements and an optical fiber array formed by arraying a plurality of optical fibers optically coupled to the plurality of light-receiving elements, respectively, characterized in that the optical module substrate is formed from an insulating ceramic.
When the optical module substrate is formed from an insulating material, no insulating film need be formed between printed interconnections and the optical module substrate, and a parasitic capacitance is prevented. In addition, when the optical module substrate is formed from a ceramic, the workability and working accuracy are ensured.
The optical module substrate of the present invention is preferably characterized in that the insulating ceramic is an insulating ceramic selected from the group consisting of alumina ceramic, zirconia ceramic, calcium titanate ceramic, silicon nitride ceramic, and aluminum nitride ceramic.
The optical module substrate of the present invention may be characterized in that the substrate comprises a reflection surface for reflecting light emerging from an end face of each of the plurality of optical fibers of the optical fiber array and making the light incident on a corresponding one of the light-receiving elements of the light-receiving element array, and the reflection surface makes an angle of substantially 45xc2x0 with respect to a mounting surface for mounting the optical fiber array.
In an optical module substrate made of silicon, it is difficult to form a reflection surface that makes an angle of 45xc2x0 with respect to the mounting surface because of the problem of crystal surface. However, in the optical module substrate made of a ceramic, the reflection surface that makes an angle of 45xc2x0 with respect to the mounting surface can be easily accurately formed, and the optical coupling efficiency between the light-receiving element array and the optical fiber array can be easily improved.
According to the present invention, there is also provided a light-emitting module characterized by comprising a light-emitting element array formed by arraying a plurality of light-emitting elements, an optical fiber array formed by arraying a plurality of optical fibers optically coupled to the plurality of light-emitting elements, respectively, an optical module substrate for mounting the light-emitting element array and the optical fiber array, a driving circuit for driving the light-emitting element array, and a base for mounting the optical module substrate and the driving circuit, wherein the optical module substrate comprises the optical module substrate formed from an insulating ceramic.
When the optical module substrate formed from an insulating ceramic is used, a parasitic capacitance is prevented, and the workability and working accuracy of the optical module substrate are ensured.
According to the present invention, there is also provided a light-receiving module characterized by comprising a light-receiving element array formed by arraying a plurality of light-receiving elements to output an electrical signal corresponding to a light-receiving amount of each of the plurality of light-receiving elements, an optical fiber array formed by arraying a plurality of optical fibers optically coupled to the plurality of light-receiving elements, respectively, an optical module substrate for mounting the light-receiving element array and the optical fiber array, an amplification circuit for amplifying the electrical signal output from the light-receiving element array, and a base for mounting the optical module substrate and the amplification circuit, wherein the optical module substrate comprises the optical module substrate formed from an insulating ceramic.
When the optical module substrate formed from an insulating ceramic is used, a parasitic capacitance is prevented, and the workability and working accuracy of the optical module substrate are ensured.